Sounds like you have a bad bug in your program. You might want to look at the later nodes in Threads memory consumption is infinite where the topic of reusing threads is discussed. I'm just guessing, because you only give a brief description of your code; but what is probably happening, is that during all those object additions to the threads, something is getting crosslinked, and won't get freed up due to the refcount problem ( search for refcount for the gory details). Then when you try to join a properly terminated thread(it must return before being joined), there is a thread safety problem.

The warning is harmless, and if your code runs fine, you just might want to let it go, or think about your design for object-thread interaction. The one thing to watch for is an unusual memory gain while running the program. That "data code o" is laying around wasting memory and causing a thread safety problem.

You said in your original node "This system has dozens of objects, each which may need to reference data from other objects. . This is probably the source of your threading bug. Many better minds than mine have tried to solve the refcount dilemma, and no success yet. I hope Perl6 has some better magic in this regard.